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Project titleNanostructured superelastic Ti-Zr-Nb alloys for bone implants with enhanced biocompatibility provided by plasma electrolytic oxidation

Research area 09 - ENGINEERING SCIENCES, 09-205 - Development of new structural materials and coatings

Keywordsnickel free shape memory alloys, severe plastic deformation, superelasticity, mechanical properties, functional properties, plasma electrolytic oxidation, coating technologies, automated technologies, bioactive coatings, corrosion resistance, biocompatibility

Annotation
The proposed project is aimed at scientific foundations of technologies for producing a composite material for bone implants based on nanostructured superelastic shape memory alloys (SMA) Ti-Zr-Nb with a biocompatible surface, combining the advantages of the mechanical behavior of a nanocrystalline substrate with high biocompatibility of the oxidized surface of the material. With the development of the medical materials science, requirements for metallic materials that should have increased functionality for bone implants are increasing. Such material, firstly, should contain exclusively biocompatible (non-toxic) components. Secondly, to ensure biomechanical compatibility, the material should have a low Young's modulus close to that of the bone tissue (up to 30 GPa). Low values of Young's modulus (40-80 GPa) and superelastic behavior close to the mechanical behavior of the bone tissue are demonstrated by the shape memory alloys, including nanostructured ones. Thirdly, the surface layer should provide a smooth transition of physicochemical properties from the metal of the implant to the human bone; this can be achieved by formation of biocompatible coatings. Recently, nickel-free SMAs based on the Ti-Zr-Nb system have been attracted an increasing interest. Due to the unique combination of biochemical and biomechanical compatibility, these alloys are the most promising among the metal biomaterials for permanent bone implants. The functional properties of the shape memory alloys can be controlled using thermomechanical processing; this allows to create a developed polygonized dislocation substructure and nanocrystalline (nanograin, nanograined or their mixture) structure in the initial high-temperature beta-phase. At the same time, it is very relevant and possible to solve the problem of additional improving of the mechanical and functional characteristics of the Ti-Zr-Nb alloys by severe plastic deformation (SPD) which would provide an opportunity to increase the service properties and durability of the implants, and contribute to their miniaturization. This can be achieved by formation of a nanostructured state in the Ti-Zr-Nb SMA by the methods of high pressure torsion (HPT), equal channel angular pressing (ECAP) and industrially promising ECAP-Conform. Earlier, ECAP and ECAP-C have shown its effectiveness in enhancing the properties of titanium and titanium alloys for medical applications, including traditional Ti-Ni SMAs. For the new Ti-Zr-Nb-based alloys, SPD has not been applied yet. Therefore, a great deal of work is required to study the characteristics of the rheological behavior of the alloy under various temperature and speed conditions by the MISiS team and to develop HPT, ECAP and ECAP-C treatment regimes and additional deformation-heat treatments by the USATU team in order to obtain the nanostructured state and enhanced material properties. The method of plasma electrolytic oxidation (PEO) has shown its effectiveness in surface treatments for implants made of titanium and titanium alloys in order to improve corrosion resistance, wear resistance and biocompatibility. The PEO coatings for the SMA of the Ti-Zr-Nb system have not been studied yet. The development of the PEO coatings for the SMAs is a promising and topical direction; automated and smart technologies are of great interest; this ensures the precise formation of the coating based on the diagnostics of its thickness, porosity and surface roughness during the treatment via electrical and optical characteristics. The tasks of the MISiS team include obtaining and certification of ingots of initial Ti-Zr-Nb alloys, their preliminary pressure processing, traditional thermomechanical processing, a comprehensive study of the structure and substructure, phase state, crystallographic texture and mechanical properties after various treatments (including that performed together with the USATU team), conducting comprehensive studies of their functional characteristics of the form restoration, including fatigue properties. Another key task of the USATU team will be the development of an automated technology for surface treatment of the Ti-Zr-Nb alloy in various structural states by using plasma electrolytic oxidation to increase the biocompatibility. The joint tasks of USATU and MISiS will also include comprehensive characterization of the surface and the barrier layer of the samples after the PEO in various regimes, comprehensive studies of biocompatibility and biocorrosion studies of the surface layer. Finally, the cooperation of the teams participating in the project will lead to the creation of a scientifically based new technology for the production of a Ti-Zr-Nb nanostructured alloy for orthopaedic and neurosurgery implants with enhanced functional properties of the base material and a PEO-treated surface that ensures long-term operation of the implants in the human body.

Expected results
During the implementation of the project, the MISiS team will produce the following main results: 1) Stress-strain diagrams and rheological models of the deformation behavior for Ti-18Nb-15Zr alloy during compression tests at various temperature and strain-rate conditions which analysis will allow determination of promising regimes for conducting severe plastic deformation. 2) Character of changes in the structural-phase state of the Ti-Zr-Nb alloy as a result of thermal-deformation effect of ECAP and HPT with post-deformation annealing by various regimes. 3) Character of changes in the mechanical and functional properties of the Ti-Zr-Nb alloy as a result of thermal-deformation effect of ECAP and HPT with post-deformation annealing by various regimes. 4) Character of crystal structure changes, description of the structural mechanisms of stress-induced transformations based on the crystal structure changes, evaluation of the theoretical recovery strain limit in nanocrystalline SMA Ti-Zr-Nb obtained by SPD. 5) Character of the omega phase formation in nanostructured Ti-Zr-Nb SMA obtained by SPD during post-deformation annealing. 6) Evaluation of the realization of the recovery strain limit and its correlation with other functional properties of nanocrystalline SMA Ti-Zr-Nb obtained by SPD. 7) Parameters of the fatigue and corrosion-fatigue behavior of nanocrystalline SMA Ti-Zr-Nb obtained by SPD. 8) Character of changes of the structure and elemental composition and microhardness in a transitional zone between the substrate and coating of the SMA Ti-Zr-Nb subjected to PEO. 9) Characteristics of the mechanical properties of the near-surface layers of nanostructured Ti-Zr-Nb SMA subjected to PEO under different conditions. 10) New schemes and optimal regimes of thermomechanical processing using the SPD methods of the Ti-Zr-Nb alloy, which ensure the formation of a nanostructured state and effectively increase the combination of functional and mechanical properties. 11) Recommendations on application of the created schemes and optimum regimes of thermomechanical treatment of the Ti-Zr-Nb alloy using SPD methods. During the implementation of the project, the USATU team will produce the following main results: 1) Optimal processing conditions for the Ti-Zr-Nb alloy by the ECAP method; this will provide the formation of a nanostructured state and effectively increase functional and mechanical properties of the alloy. 2) The SPD samples of the Ti-Zr-Nb alloy in the nanostructured state with enhanced functional and mechanical properties. 3) Patterns of changes in the structure, physical and mechanical properties of the Ti-Zr-Nb alloy under the influence of SPD according to various modes, additional deformation-heat treatment after SPD (together with MISiS). 4) The samples with biocompatible coatings obtained by PEO method for the Ti-Zr-Nb alloy after standard thermal-mechanical treatment (TMT) and in the nanostructured state after SPD. 5) Regularities of the structural-phase composition formation and morphology of PEO coatings, including those containing calcium phosphates, obtained in various PEO modes on the Ti-Zr-Nb alloy after standard TMT and in the nanostructured state (together with MISiS). 6) Parameters of electrochemical and gravimetric corrosion characteristics of nanostructured and TMT samples with PEO coatings, including corrosion-fatigue behavior (together with MISiS). 7) Results of in vitro studies of the samples with PEO coatings obtained on the Ti-Zr-Nb alloy after standard TMT and in the nanostructured state after SPD, showing an increase in biocompatibility of the surface compared to the uncoated alloy. 8) Technological regimes of obtaining PEO coatings that provide the optimal combination of physical, chemical and biological properties of the samples of the Ti-Zr-Nb alloy after standard TMT and in the nanostructured state. 9) Approaches to the controlled formation of biocompatible PEO coatings on Ti-Zr-Nb SMA based on in situ diagnostics of the PEO process using impedance and optical emission spectroscopy, which provides information about the thickness, porosity of the coating, and surface roughness during the PEO. 10) Demonstrational experimental automated installation for plasma electrolytic oxidation, which allows formation of biocompatible PEO coatings on prototype implants made of SMA Ti-Nb-Zr. As a result of this interdisciplinary project, during the joint work of MISiS and USATU, scientific and technical foundations will be developed for the technology of producing the Ti-Zr-Nb alloy in nanostructured state with advanced functional and mechanical properties and coatings with enhanced biocompatibility provided by plasma electrolytic oxidation. The Ti-Zr-Nb nanostructured alloy and its TMT, SPD and PEO treatment modes can be further used for the production of permanent bone implants for orthopedics and neurosurgery with enhanced service properties. This complex research is for the first time and it has significant relevance for engineering and physical sciences at the all-Russian and all-world level. The expected results of this interdisciplinary project will have a significant synergistic effect, scientific and social significance and they will serve as the basis for the modern technology development for the production of new generation of implants for orthopedics and neurosurgery. The authors suggest that similar studies are already being carried out in the world, or will be undertaken in the near future.

Annotation of the results obtained in 2023
According to the work plan, in the fourth year of the project, the development of scientific and technical fundamentals of technologies for producing Ti-Zr-Nb alloy in a nanostructured state with increased functional and mechanical properties and with coatings obtained by plasma electrolytic oxidation (PEO) continued. The work was carried out jointly with the NUST MISIS team. Additional studies have been carried out on the influence of the equal-channel angular pressing method according to the conformal scheme (ECAP-K, which is promising for producing long workpieces) on the Ti-Zr-Nb alloy. More effective for obtaining a more durable state (on existing equipment) is ECAP-Conform in a mode where the initial rod was preheated to a temperature of 550 C in an external furnace and subjected to two ECAP-K cycles in a row on equipment heated to 450 °C. Analysis of X-ray diffraction data allows us to state that after ECAP-C in the modes used, the main phase remains the beta phase (which is necessary for the implementation of functional properties). As a result of ECAP-Conform, the yield strength of the alloy increased from 510 to 580 MPa and a significant plasticity resource remained (13%). After annealing at 350 °C for 30 min in the ECAP-Conform condition, the strength increased to 1270 MPa, and the ductility dropped to 2.5%. This is apparently the result of aging and the formation of omega-phase nanoparticles in an ultrafine-grained structure. The greatest complex of strength and functional properties was achieved by “traditional” ECAP at a temperature of 500° with a number of cycles n=4. At a temperature of 500 °C, phase transformations with the formation of alpha and omega phases are suppressed. After such treatment, an ultra-fine-grained structure of the alloy is formed, the state with the main beta phase is preserved, the strength has reached 825 MPa and (according to NUST MISIS partners) the highest values of reversible deformation are achieved - 3% (necessary for the functional use of the alloy). A method has been developed for the controlled formation of a PEO coating, which ensures precise achievement of the required values of porosity, roughness and coating thickness, based on in situ diagnostics based on electrical and optical characteristics. The method is implemented through a new feedback loop in the PEO process control system, which provides indirect measurement of unobservable parameters - porosity, roughness and coating thickness, based on the measurement of observable parameters - optical radiation intensity, voltage, current and others and the subsequent application of a regression diagnostic model, linking the specified parameters. The controlled variable is the duration of the PEO process, carried out under optimal conditions determined at the previous stages (electrolyte, pulse voltage, frequency and other characteristics). Variation in the preparation of the initial surface, drift in the properties of the electrolyte, and the influence of random factors will change the duration of the process required to achieve the target coating thickness. The roughness and porosity of the coating are limitations. The structure of an automated control system for the technological process of plasma-electrolytic oxidation and an algorithm for its operation have been developed. The method is easily implemented using a digital PEO process control system and allows you to signal to the operator that the required coating thickness has been reached. Statistical regression models for diagnosing porosity, roughness and coating thickness were developed based on the results of constructing neural network models on the state space of the PEO process, modeled with a treatment duration step of 1 s. As a result, the most correlated parameters were established and regression models were built that connect the parameters of the surface state and the electrical and optical characteristics. The coefficient of determination for diagnostic regression equations was 0.96 or higher. The resulting models are suitable (subject to repeating the calibration) for any PEO installation and do not require the use of neural network models in the diagnostic circuit, which are characterized by the complexity of software implementation and the complexity of reconfiguration. An automated PEO installation of sufficient power (35 kW) has been designed and created to process prototype implants. The installation allows to supply voltage pulses (positive - from 0 to 700 V, negative from 0 to 200 V) with a frequency from 0 to 15 kHz, duty cycle from 1 to 100%. The maximum current is 100 A. The processed surface area is up to 200 cm2. The electrolytic bath volume is 30 l. Electrolyte temperature 20±1 °C. Voltage and current stabilization modes are provided. The installation is controlled from a personal computer, which provides both software control of processing modes and diagnostics of the surface properties during plasma-electrolytic oxidation.

Publications

1. Farrakhov R.G., Aubakirova V.R., Zaynullina L.I., Parfenov E.V. Влияние ПЭО покрытия на коррозионные свойства поверхности сплава Ti-Zr-Nb Белкинские чтения : материалы Всероссийской научно-методической конференции (г. Кострома, 25–26 апреля 2023 г.). – Кострома : Костромской государственный университет, 2023., Белкинские чтения : материалы Всероссийской научно-методической конференции (г. Кострома, 25–26 апреля 2023 г.). – Кострома : Костромской государственный университет, 2023. С. 145-150 (year - 2023)

2. Gunderov, D.; Kim, K.; Gunderova, S.; Churakova, A.; Lebedev, Y.; Nafikov, R.; Derkach, M.; Lukashevich, K.; Sheremetyev, V.; Prokoshkin, S. Effect of High-Pressure Torsion and Annealing on the Structure, Phase Composition, and Microhardness of the Ti-18Zr-15Nb (at. %) Alloy Materials, Materials 2023, 16, 1754 (year - 2023) https://doi.org/10.3390/ma16041754

3. Zaynullina L.I., Farrakhov R.G., Ramazanov I.A., Dyuryagin V.S., Parfenov E.V. Влияние пескоструйной обработки и плазменно-электролитического оксидирования на качество поверхности дентальных имплантатов Современные технологии в медицине, - (year - 2023)

4. Zaynullina L.I., Sharipov I.Z., Gunderov D.V., Farrakhov R.G., Parfenov E.V. Влияние циклического нагрева на свойства ПЭО-покрытий на сплаве Ti-18Zr-15Nb в УМЗ состоянии Вестник УГАТУ, Вестник УГАТУ, 2023. Т. 27, № 3 (101). С. 58–65 (year - 2023)

5. Farrakhov R.G., Aubakirova V.R., Sabitov A.R., Parfenov E.V. Изучение ПЭО-покрытий на поверхности сплавов Ti-Zr-Nb методами in-situ и ex-situ импедансной спектроскопии Кайбышевские чтения: сборник материалов Третьей Международной школы-конференции молодых ученых (г. Уфа, 16-20 октября 2023 г.). – Уфа: РИЦ УУНиТ, 2023., Кайбышевские чтения: сборник материалов Третьей Международной школы-конференции молодых ученых (г. Уфа, 16-20 октября 2023 г.). – Уфа: РИЦ УУНиТ, 2023. С. 141 (year - 2023)

6. Parfenov E.V., Gunderov D.V., Sheremetyev V.A., Nagumothu Rameshbabu Biomimetic PEO coatings for implants made of nanostructured titanium alloys Conference Proceedings of Nano SPD8 – 8th International Conference on Nanostructured Materials by Severe Plastic Deformation, Indian Institute of Science, Bangalore, India, Conference Proceedings of Nano SPD8 – 8th International Conference on Nanostructured Materials by Severe Plastic Deformation, Indian Institute of Science, Bangalore, India. P. 22 (year - 2023)

7. Parfenov E.V., Parfenova L.V. Развитие медицинских имплантируемых материалов и современные тренды их развития Кайбышевские чтения: сборник материалов Третьей Международной школы-конференции молодых ученых (г. Уфа, 16-20 октября 2023 г.). – Уфа: РИЦ УУНиТ, 2023., Кайбышевские чтения: сборник материалов Третьей Международной школы-конференции молодых ученых (г. Уфа, 16-20 октября 2023 г.). – Уфа: РИЦ УУНиТ, 2023. С. 106 (year - 2023)

8. Parfenov E.V., Parfenova L.V. Advanced coatings for next generation medical implants Proceedings of 2023 Sino-Russia Scientific Conference on Advanced Materials and Technologies. Changzhou University, China., Proceedings of 2023 Sino-Russia Scientific Conference on Advanced Materials and Technologies. Changzhou University, China. P. 5. (year - 2023)

Annotation of the results obtained in 2020
According to the work plan, in the first year of the project, the initial samples of the Ti-18Zr-15Nb alloy were obtained from the NITU MISiS team after thermomechanical treatment (TMT). Experimental nanostructured disk samples of Ti – Zr – Nb with extremely fine grains were obtained by the severe plastic deformation (SPD) method known as high pressure torsion (HPT) as well as by the new method proposed by the authors of the project - “Accumulating High Pressure Torsion (AC HPT)”, which makes it possible to achieve high degrees of deformation in solid materials. The number of revolutions of the HPT and AC HPT varied from n = 1 to n = 10 at room temperature. Large-size SPD Ti18Zr15Nb samples were obtained by equal-channel angular pressing (ECAP). The rods were subjected to ECAP at a temperature of T = 250 C, with the number of cycles n = 4 and n = 7. An ECAP tooling was used with a channel intersection angle of 120 deg and a diameter of 10 mm. As a result, a series of solid ECAP samples with a diameter of 10 mm and a length of about 60 mm were obtained for studying the mechanical properties, microstructure, testing the PEO coatings, and to transfer the sample to partners at NITU MISIS. Studies of the structure and mechanical properties of samples subjected to SPD in various modes have been carried out. TEM studies have shown that as a result of HPT (n = 5), a refined nanostructure with a grain / subgrain size of 10-30 nm is formed in the alloy; as a result of ECAP, a nanostructured state with a grain size of 200-300 nm is formed, the size of subgrains is about 50 nm. The data of mechanical tests showed that as a result of HPT, the microhardness of the alloy increases significantly. The microhardness, strength, and especially the yield stress of the alloy are also significantly increased as a result of ECAP. The yield stress (St) increases from the initial 510 MPa after TMT (up to d = 80 mm) to 855 MPa after ECAP n = 4 and to 960 MPa after ECAP n = 7. Analysis of X-ray structural analysis and TEM data shows that BCC beta is the main phase in the initial Ti-18Zr-15Nb alloy and after HPT and ECAP. A feature of the Ti18Zr15Nb alloy is the presence of shape memory effects in the beta state. An increase in the yield stress of the Ti18Zr15Nb alloy after ECAP together with the retention of the beta state allows one to expect an increase in the functional properties of the alloy. According to the work plan, on the initial samples made of Ti-18Zr-15Nb alloy with preliminary thermomechanical treatment, a coating was obtained by plasma electrolytic oxidation (PEO). PEO was carried out in a pulsed bipolar mode with voltage stabilization. An aqueous solution of 20 g / L Na3PO4 · 12H2O was used as the base electrolyte; its temperature was kept constant at 20 ± 1 ° С. Three optimization cycles were carried out – first, electrical characteristics, second, the composition of the electrolyte, and, third, by the introduction of a bio-additive that ensures the formation of calcium phosphate coatings. The PEO coating obtained using a phosphate electrolyte has a uniform surface. The coating thickness is 17-21 microns. Due to the features of the oxidation process, the resulting surface layer has round pores ranging in size from 0.5 to 10 microns and elongated pores with a width of 3-5 microns and a length of up to 30 microns. Analysis of the EDS mapping data shows that the coating contains Ti, Zr and Nb oxides; Ti is evenly distributed over the surface, while Zr, Nb and O appear less in the pores of the coating. PEO coatings obtained at a frequency of 1000 Hz are more homogeneous compared to that obtained at the frequency of 300 Hz, which feature surface defects containing a significant amount of P. As a result of the X-ray diffractometry, oxides TiO2 (rutile, anatase), ZrO2 (m, t -phases), Nb2O5, NbO2 in different proportions were identified depending on the processing mode. Investigation of the corrosion potential and corrosion current shows that the coatings provide surface passivation compared to the substrate material. For the frequency of 1000 Hz, the corrosion current is lower and the polarization resistance is higher than for the frequency of 300 Hz and the substrate. Therefore, to optimize the composition of the electrolyte, the electrical mode with a frequency of 1000 Hz was chosen. The alkaline phosphate-silicate electrolyte APS was taken as the base electrolyte. The concentrations of phosphate, silicate, glycerol, and boric acid were varied; the thickness of the coatings, porosity, elemental and phase composition, and corrosion characteristics were analyzed. It was shown that the best combination of parameters is exhibited by the coatings obtained in the APSB electrolyte (1 g / L NaOH, 10 g / L Na2SiO3 * 5H2O, 10 g / L Na3PO4 * 12H2O, 1 g / L H3BO3). With a porosity of 7.5%, this coating has a thickness of 8.3 μm, contains 54% anatase, 4% rutile and 42% SiO2 in the crystalline phase. This provides a minimum corrosion current of 0.026 μA / cm2, which is 1.3 times less than this parameter for the alloy. In the production of calcium phosphate PEO coatings, calcium acetate (Ca (CH3COO) 2) 25 g / L was used as an additive, which showed promising characteristics of the coatings. As a result, it was shown that the sample obtained in the phosphate electrolyte with calcium acetate possesses the best corrosion resistance. The treatment in this electrolyte passivates the surface, as evidenced by the higher potential of free corrosion and an order of magnitude lower corrosion current compared to the Ti18Zr15Nb alloy. In this coating, a calcium-containing crystalline phase, perovskite CaTiO3, was identified, which contributes to an increase in the biocompatibility of the surface.

Publications

1. Gunderov D.V., Prokoshkin S.D., Churakova A.A., Sheremetyev, V.A., Ramazanov I.A. Effect of HPT and accumulative HPT on structure formation and microhardness of the novel Ti18Zr15Nb alloy Materials Letters, Gunderov D., Prokoshkin S., Churakova A., Sheremetyev V., Ramazanov I. Effect of HPT and accumulative HPT on structure formation and microhardness of the novel Ti18Zr15Nb alloy // Materials Letters. ‒ 2021. ‒ Vol. 283. - P. 128819 (year - 2021) https://doi.org/10.1016/j.matlet.2020.128819

2. Churakova A.A., Gunderov D.V., Prokoshkin S.D., Sheremetyev V.A., Lisboa Filho P.N., Alves Claro A.P.R. Подвергнутые ИПД титановые сплавы Ti18Zr15Nb и Ti10Mo8Nb6Zr ПОЛУЧЕНИЕ, СТРУКТУРА И СВОЙСТВА ВЫСОКОЭНТРОПИЙНЫХ МАТЕРИАЛОВ: Тезисы международной конференции и школы молодых ученых. 14-16 октября 2020 г. - Издательство: ООО Эпицентр (Белгород), С. 104 (year - 2020)

3. Shechtman S.R., Farrakhov R.G., Ramazanov I.A., E.V. Parfenov Исследование защитных ПЭО-покрытий на титановом сплаве с памятью формы для изделий медицинского назначения Ультрамелкозернистые и наноструктурные материалы: Сборник трудов Открытой школы-конференции стран СНГ. 05-09 октября 2020 г., г. Уфа. - Уфа: РИЦ БашГУ, 2020, С. 57-59 (year - 2020)

Annotation of the results obtained in 2021
This project is aimed at solving the scientific problem of obtaining a new biomedical nanostructured superelastic titanium alloy of the Ti-Zr-Nb system with high performance properties due to the application of methods of severe plastic deformation and surface modification for its use as a material for implantable devices with a high level of biocompatibility. Within the second year of the project, the following main results were obtained: 1) On the basis of the established regularities of the nanostructure formation and analysis of mechanical characteristics, the optimal regime of severe plastic deformation was determined (8 passes of equal channel angular pressing (ECAP) at a temperature of 500 ºС with an angle of the channel intersection 120º); the regime can be successfully applied to rods of Ti-18Zr-15Nb alloy with a diameter of 20 mm to produce the following mechanical properties: σv = 910 ± 10 MPa, σ02 = 880 ± 15 MPa, δ = 6%. 2) According to the results of the study of the temperature and treatment time effect on the nanostructure of the Ti-18Zr-15Nb alloy obtained by ECAP, a regime of a short-term annealing (550°C; 2.5 min) was revealed; the use of this treatment leads to a 2-fold increase in the plasticity of the material under study - from 6 up to 12%. At the same time, according to the results of a study by colleagues from NUST MISiS, at this annealing regime in the deformed Ti-18Zr-15Nb alloy, the maximum value of reversible deformation is observed. 3) The results of a comprehensive study of the formation of the structural-phase composition and tribological properties were obtained for plasma electrolytic oxidation (PEO) coatings on Ti-18Zr-15Nb alloy samples in coarse-grained and nanostructural states in the electrolytes based on 20 g / L Na3PO4 12H2O + 25 g / L calcium acetate with the addition of Na2SiO3 and H3BO3. It was found that the treatment in the phosphate electrolyte with the addition of the H3BO3 leads to the formation of high temperature oxide phases of titanium, zirconium and niobium in the coating; this significantly increases the corrosion properties of the coating. It was found that the nanostructured Ti-18Zr-15Nb alloy treated in this electrolyte demonstrates the highest adhesive strength of the coating. 4) The effect of the PEO coating on the corrosion properties of coarse-grained and nanostructured Ti-18Zr-15Nb alloy has been studied. The positive effect of the surface modification by the PEO method on the corrosion resistance of the material in the both states appears due to the passivation of the coating surface in all investigated electrolytes. The difference in the kinetics of corrosion processes of the samples after the PEO treatment has been established by the means of electrochemical impedance spectroscopy which revealed the different morphology of the coatings and their structure. The best results were obtained in the electrolyte based on 20 g / L Na3PO4 12H2O + 25 g / L calcium acetate with the addition of 1 g / L H3BO3 for the material in the both structural states. 5) It is planned to prove biocompatibility in vitro for samples obtained using optimized regimes of the nanostructuring and plasma electrolytic oxidation during the next year of the project.

Publications

1. Churakova A.A., Gunderov D.V., Raab G.I., Prokoshkin S.D., Sheremetyev V.A., Filho P.N.L., Pedro J., Claro A.P.R.A. Influence of ECAP on the structure and properties of Ti18Zr15Nb and Ti10Mo8Nb6Zr alloys for medical application IOP Conf. Ser. Mater. Sci. Eng., IOP Conference Series: Materials Science and Engineering, 1014 (1), статья № 012006 (year - 2021) https://doi.org/10.1088/1757-899X/1014/1/012006

2. Farrakhov R.G., Melnichuk O.V., Parfenov E.V., Mukaeva V.R., Raab A.G., Sheremetyev V.A., Zhukova Y.S., Prokoshkin S.D. Comparison of Biocompatible Coatings Produced by Plasma Electrolytic Oxidation on cp-Ti and Ti-Zr-Nb Superelastic Alloy Coatings, Coatings, 11 (2021) 401. (year - 2021) https://doi.org/10.3390/coatings11040401

3. Mukaeva V.R., Gorbatkov M.V., Farrakhov R.G., Lazarev D.M., Stotskiy A.G., Parfenov E.V. Advanced plasma electrolysis research equipment with in-situ process diagnostics Proceedings - ICOECS 2020, 2020 International Conference on Electrotechnical Complexes and Systems (ICOECS), 2020, pp. 9278498. (year - 2020) https://doi.org/10.1109/ICOECS50468.2020.9278498

4. Shechtman S.R., Farrakhov R.G., Ramazanov I.A., Sheremetyev V.A., Parfenov E.V. Protective PEO-coatings on titanium shape memory alloy for medical implants IOP Conference Series: Materials Science and Engineering, Shechtman, S.R., Farrakhov, R.G., Ramazanov, I.A., Sheremetyev, V.A., Parfenov, E.V. Protective PEO-coatings on titanium shape memory alloy for medical implants (2020) IOP Conference Series: Materials Science and Engineering, 1008 (1), статья № 012016 (year - 2020) https://doi.org/10.1088/1757-899X/1008/1/012016

5. - Башкирские учёные создают уникальные импланты с живыми клетками. Вот их история UTV.ru, - (year - )

Annotation of the results obtained in 2022
According to the work plan, in the third year of the project, the development of scientific and technical foundations for technologies for obtaining Ti-Zr-Nb alloy in a nanostructured state with enhanced functional and mechanical properties based on the formation of coatings by plasma-electrolytic oxidation (PEO) was carried out together with the NUST MISiS team. After equal-channel angular pressing (ECAP) at a number of revolutions n = 4 and a temperature of 500 °C, an ultrafine-grained structure of the Ti-Zr-Nb alloy was obtained. A deformed dynamically polygonized β-phase substructure was formed in the alloy, the subgrain state of which has a size of structural elements (subgrains) of about 500–1000 nm. These structural elements also have an internal substructure. A good set of mechanical properties was achieved - high strength properties, yield strength with good plasticity (825 MPa, 663 MPa and 16% for ECAP 500 °C n=4). The nanocrystalline state of the Ti-Zr-Nb alloy was also achieved by the method of high pressure torsion (HPT). A structure with a high dislocation density and a grain size of less than 100 nm was formed. To obtain long workpieces, the ECAP-Conform method for the Ti-Zr-Nb alloy was used, experimental samples were obtained in various modes. An analysis of the structure and mechanical properties showed that after ECAP-Conform in one of the regimes, the structure was noticeably refined, and the size of grains/structural elements noticeably decreased. Inside the original grains, microbands and packets of microbands are observed that intersect the original grains. However, the level of properties achieved by the ECAP-Conform method is lower than with the traditional ECAP, thus, optimization of the ECAP-Conform modes is necessary to achieve higher strength. To optimize the technological mode of PEO, regression mathematical models of the coating thickness, surface roughness, corrosion current and polarization resistance were built. In the simulation, a two-factor three-level experimental design was used. The concentrations of the electrolyte components were the factors of the experiment, since it was shown in previous studies that the electric mode has a lesser effect on the quality of the coating than the composition of the electrolyte. The optimization criterion was the parameter of electrochemical corrosion - the maximum polarization resistance. The optimal electrolyte according to this criterion is 20 g/L Na3PO4 12H2O + 25 g/L Ca(CH3COO)2 + 1 g/L H3BO3 (electrolyte PB). The optimal duration of PEO (120 s) is substantiated, which makes it possible to form the most corrosion-resistant coating of sufficient thickness, porosity, and roughness. A route technological process for PEO has been developed, which ensures the production of coatings with optimal characteristics according to the selected criterion. Improved methods for diagnosing coating characteristics based on the analysis of the electrical and optical characteristics of the PEO process have been obtained. A stable relationship between the growth rate of the coating thickness and the average intensity of microdischarge radiation obtained from the spectrometer is revealed. Indirect velocity measurement makes it possible to calculate the coating thickness during PEO with an error of 10%, corresponding to the non-uniformity of the coating thickness introduced by the roughness. The application of the proposed diagnostic method will make it possible to stop the PEO process in time, which will improve the quality of the resulting coatings. The results of in situ impedance spectroscopy are analyzed and an electrical equivalent circuit of the PEO process is proposed. It is shown that the equivalent circuit can be a tool for evaluating the stages of the process and the thickness of the coating. At the beginning of the process, the alloy is anodized and a defect-free barrier layer grows, while spark discharges are not observed. Therefore, the impedance spectrum corresponding to a given time interval is approximated by a circuit with one time constant - the Randles circuit. Further, during processing, microdischarges occur and the upper porous layer of the coating is formed. This stage was approximated by a scheme with two time constants - a ladder scheme. Based on the equivalent circuit, the mechanism of the process is substantiated, including the development of microdischarges in the inner barrier layer of the coating, since for this part the charge transfer resistance is negative; this behavior is characteristic of the sections corresponding to the microdischarge plasma. Using the methods of in-situ and ex-situ impedance spectroscopy, structurally identical electrical equivalent circuits were obtained, which confirms the proposed mechanism of the process. The calculation of the numerical values of the parameters of the equivalent circuit showed that the values of the resistance and capacitance of the coating make it possible to estimate the thickness of the coating and other parameters correlated with it, with an error of 10%. Timely shutdown of the technological process makes it possible to prevent excessive energy consumption and ensure the required quality of the coating. In vitro studies of the biocompatibility of Ti-Zr-Nb samples after thermomechanical treatment and nanostructuring, before and after PEO in optimal conditions were carried out. For the tests, mesenchymal stem cells from rat adipose tissue were cultured. The analysis of cell proliferative activity showed that all materials and coatings are non-cytotoxic and, therefore, they can be used for implant applications. The following web pages are devoted to the project: https://www.ugatu.su/news/get/uchenye-ugatu-sozdali-importozameshayushie-dentalnye-implantaty/ https://minobrnauki.gov.ru/press-center/news/nauka/59852/?lang=ru https://www.gazeta.ru/science/news/2022/10/13/18788587.shtml https://pravitelstvorb.ru/news/19126/ https://t.me/eurasian_noc/1949 https://utv.ru/material/ufimskie-uchenye-izobreli-unikalnye-zubnye-implanty/ https://www.youtube.com/watch?v=DoCySurps9o&t=6s

Publications

1. Farrakhov R.G., Aubakirova V.R., Gorbatkov M.V., Lebedev Yu.A., Parfenov E.V. Формирование покрытий методом плазменно-электролитического оксидирования на сверхупругом сплаве Ti–18Zr–15Nb в кальцийсодержащих электролитах Frontier Materials & Technologies, Frontier Materials & Technologies. 2022. № 3. С. 56–67. (year - 2022) https://doi.org/10.18323/2782-4039-2022-3-2-56-67

2. Gunderov D.V., Churakova A.A., Polyakov A.V., Raab A.G., Gunderova S.D., Lebedev Yu.A., Ana Paula Rosifini Alves Claro The Influence of Equal Channel Angular Pressing on Structure and Mechanical Properties of New β-Ti Alloy Ti–10Mo–8Nb–6Zr Известия вузов. Цветная металлургия / Russian Journal of Non-Ferrous Metals, Известия вузов. Цветная металлургия. 2022. Т. 28. No. 6. С. 49–57 (year - 2022)

3. Gunderov D.V., Kim K.A., Churakova A.A., Sheremetyev V.A., Derkach M.A., Lebedev Yu. A., Raab A.G. Структура и механические свойства сплава Ti–18Zr–15Nb, подвергнутого равноканальному угловому прессованию при разных температурах Физика металлов и металловедение / Physics of Metals and Metallography, ФИЗИКА МЕТАЛЛОВ И МЕТАЛЛОВЕДЕНИЕ, 2022, том 123, № 10, с. 1–10 (year - 2022) https://doi.org/10.31857/S0015323022600575

4. Churakova A.A., Kayumova E.M., Gunderov D.V. Термоциклирование в диапазоне температур мартенситных превращений как способ повышения механических свойств в сплаве TiNi IV Байкальский материаловедческий форум: Материалы Всероссийской научной конференции с международным участием, IV Байкальский материаловедческий форум: Материалы Всероссийской научной конференции с международным участием (Улан-Удэ, 1-7 июля 2022 г.). - Улан-Удэ, 2022. - С. 588-590 (year - 2022)

5. Parfenov E.V., Parfenova L.V. Биомиметические покрытия на основе плазменно-электролитического оксидирования и функциональных органических молекул для имплантатов из титановых сплавов Гены & Клетки / Genes and Cells, Гены & Клетки XVII, № 3, 2022, C. 173-174 (year - 2022)

6. - Ученые УГАТУ создали импортозамещающие дентальные имплантаты Новости УГАТУ, - (year - )

7. - В России импортозаместили дентальные имплантаты Пресс-центр Минобрнауки, Исследование выполнено в рамках проекта Евразийского Научно-образовательного центра (НОЦ) мирового уровня «Восстановительная и регенеративная медицина» при поддержке Российского научного фонда. (year - )

8. - В России создали костные импланты, которые приживаются в два раза быстрее импортных Газета.ru, - (year - )

9. - Ученые авиационного вуза Евразийского НОЦ создали импортозамещающие дентальные имплантаты Новости Правительства Республики Башкортостан, Исследование выполнено в рамках проекта Евразийского НОЦ мирового уровня «Восстановительная и регенеративная медицина» при поддержке Российского научного фонда, его результаты опубликованы в ряде международных изданий. (year - )

10. - Ученые авиационного вуза Евразийского НОЦ создали импортозамещающие дентальные имплантаты Телеграм / Евразийский НОЦ мирового уровня, Исследование выполнено в рамках проекта Евразийского НОЦ мирового уровня «Восстановительная и регенеративная медицина» при поддержке Российского научного фонда, его результаты опубликованы в ряде международных изданий. (year - )

11. - Уфимские ученые изобрели уникальные зубные импланты Телекомпания UTV, Евгений Парфёнов, руководитель проекта РНФ 20-69-47029 (year - )

12. - Уфимские учёные изобрели уникальные зубные импланты. Заменят ли они зарубежные? UTV. Новости Уфы и Башкирии, Евгений Парфёнов, руководитель проекта РНФ 20-69-47029 (year - )